Uttarakhand PMT Uttarakhand PMT Solved Paper-2005

  • question_answer A source is moving towards an observer with a speed of 20 m/s and having frequency of 240 Hz. The observer now moving towards the source with a speed of 20 m/s. Apparent frequency heard by the observer, is (velocity of sound = 340 m/s):

    A)  270 Hz         

    B)  540 Hz

    C)  135 Hz          

    D)  370 Hz

    Correct Answer: A

    Solution :

     Here: Speed of the source \[{{V}_{s}}=20m/s\] Frequency of sound \[v=240\text{ }Hz\] Speed of the sound\[v=340\text{ }m/s\] The apparent frequency heard by observer is given by \[n=\left( \frac{\upsilon +{{\upsilon }_{0}}}{\upsilon -{{\upsilon }_{s}}} \right)n\] Or \[n=\frac{340+20}{340-20}\times 240\] Or \[n=\frac{360\times 240}{320}=270\,Hz\]

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